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Undeliverable Emails: What, Why and How

When your email is undeliverable, it simply means your email never actually go to your intended recipient.

In this article, we will look at some of the common reasons why emails are undeliverable or bounced and what you can do about it.

  1. A non-existent email address

    This is probably the most common reason why your email is bounced.

    Things you can check for:

    • Have you entered the correct recipient email address? Check for typos and possible mistakes.
    • Is the recipient email address valid? Perhaps the person has already left the company and the email address is no longer valid?
  2. Undeliverable email

    If the email is bounced back to you as “undeliverable” it could mean that the receiving email server is temporarily unavailable, overloaded or simply couldn’t be found.

    If the server has crashed or is under maintenance (in other words, temporarily unavailable), you will need to wait to send the email again.

    However, fi the email keeps bouncing back, it could mean the server is gone for good.

  3. Mailbox full

    If your recipient has a lot of emails in their inbox they will not be able to receive further emails until storage space is cleared up – your emails will bounce back until there is space for them.

    The best way to rule this reason out is to follow up with your recipient.

  4. Auto-response

    This, technically, is not an undeliverable case as your email was successfully sent to your recipient’s inbox.

  5. Blocked email

    In this case, the receiving email server has blocked your email. This happens if the receiving email server (or recipient email account) as filtering rules in place. To resolve this issue, you will need to get in touch with your recipient and request them or their system administrators to unlock your mail server IP address.

People who try to send me emails keep getting “Undeliverable” messages.

The first step is to find out why the emails were bounced. You will need to ask the sender(s) for a copy of the full email header because that’s where you will find clues to resolve the issue.

Once they have sent you a copy of the full email header, you can then determine why the email was bounced.

For example, if you see the following error message in the email header,

550 Requested action not take: mailbox unavailable

You will need to verify that the sender has entered your email address correctly.

However, if the sender is getting bounce message with a “550 5 2 1 mail from refused spam site” error message or similar message, it means that your email address has been blacklisted. You will need to contact us immediately so we can further assist you.

Why am I getting “undeliverable” email about emails I didn’t send?

Unfortunately, spammers might have gotten a hold of your email address.

Spammers often use a real address as the “from” address when they send out mail. When the from address looks like a real address (because it is), the recipients are more likely to read the message.

When a spammer sends out a message to millions of addresses, there’s bound to be a few if not more address that will not work because these addresses no longer exist or the mailbox is full. These bounce errors will then be sent to the email address that is used as the “from” address – which is you.

While this is annoying, it does not mean your account has been hacked. When you send mail from an email client, you can change the “from” address to anything you want. That’s what the spammers are doing.